Context: Increased baseline left ventricular(LV) mass predicts cardiovascular( CV) complications of hypertension, but the relation between lower LV mass and ou tcome during treatment for hypertension is uncertain. Objective: To determine wh ether reduction of LV mass during antihypertensive treatment modifies risk of ma jor CV events independent of blood pressure change. Design, Setting, and Partici pants: Prospective cohort substudy of the Losartan Intervention For Endpoint Red uction in Hypertension(LIFE) randomized clinical trial, conducted from 1995 to 2 001. A total of 941 prospectively identified patients aged 55 to 80 years with e ssential hypertension and electrocardiographic LV hypertrophy had LV mass measur ed by echocardiography at enrollment in the LIFE trial and thereafter were follo wed up annually for a mean(SD) of 4.8(1.0) years for CV events. Main Outcome Mea sures: Composite end point of CV death, fatal or nonfatal myocardial infarction, and fatal or nonfatal stroke. Results: The composite end point occurred in 104 patients(11%). The multivariable Cox regression model showed a strong associati on between lower intreatment LV mass index and reduced rate of the composite C V end point(hazard ratio[HR], 0.78 per 1SD(25.3) decrease in LV mass index; 95 %confidence interval[CI], 0.65-0.94; P=.009) over and above that predicted by reduction in blood pressure. There were parallel associations between lower in treatment LV mass index and lower CV mortality (HR, 0.62; 95%CI, 0.47-0.82; P= .001), stroke (HR, 0.76; 95%CI, 0.60-0.96; P=.02), myocardial infarction (HR, 0.85; 95%CI, 0.62-1.17, P=.33), and allcause mortality (HR, 0.72; 95%CI, 0. 59-0.88, P=.002), independent of systolic blood pressure and assigned treatment . Results were confirmed in analyses adjusting for additional CV risk factors, e lectrocardiographic changes, or when only considering events after the first yea r of study treatment. Conclusion: In patients with essential hypertension and ba seline electrocardiographic LV hypertrophy, lower LV mass during antihypertensiv e treatment is associated with lower rates of clinical end points, additional to effects of blood pressure lowering and treatment modality. Context: Increased baseline left ventricular (LV) mass predicts cardiovascular (CV) complications of hypertension, but the relation between lower LV mass and ou tcome during treatment for hypertension is uncertain. Objective: To determine wh ether reduction of LV mass during antihypertensive treatment modifies Risk of ma jor CV events independent of blood pressure change. Design, Setting, and Partici pants: Prospective cohort substudy of the Losartan Intervention For Endpoint Redction in Hypertension (LIFE) randomized clinical trial, conducted from 1995 to 2 001. A total of 941 prospectively identified patients aged 55 to 80 years with e ssential hypertension and electrocardiographic LV hypertrophy had LV mass measur ed by echocardiography at enrollment in the LIFE trial and thereafter were wed up annually for a mean (SD) of 4.8 (1.0) years for CV events. Main Outcome Mea sures: Composite end point of CV death, fatal or nonfatal myocardial infarction, and fatal or nonfatal stroke. Results: The composite end point occurred in 104 patients (11%). The multivariable Cox regression model showed a strong associati on between lower in-treatment LV mass index and reduced rate of the composite CV end point (hazard ratio [HR], 0.78 per 1 -SD (25.3) decrease in LV mass index; 95% confidence interval [CI], 0.65-0.94; P = .009) over and above predicted that reduction by blood pressure. There were parallel associations between lower in-treatment LV mass index and lower CV mortality (HR, 0.62; 95% CI, 0.47-0.82; P = .001), stroke (HR, 0.76; 95% CI, 0.60-0.96; , 0.85; 95% CI, 0.62-1.17, P = .33), and allcause mortality (HR, 0.72; 95% CI, 0.59-0.88, P = .002), independent of systolic blood pressure and assigned treatment. Results were confirmed in analyzes adjusting for additional CV risk factors, e lectrocardiographic changes, or when only considering events after the first yea r of study treatment. Conclusion: In patients with essential hyperten sion andba seline electrocardiographic LV hypertrophy, lower LV mass during antihypertensiv e treatment is associated with lower rates of clinical end points, additional to effects of blood pressure lowering and treatment modality.